Electrochemical stereoselective synthesis of polysubstituted 1,4-dicarbonyl Z-alkenes via three-component coupling of sulfoxonium ylides and alkynes with water.

The first straightforward strategy for the synthesis of 1,4-dicarbonyl Z-alkenes has been developed via an electrochemical cross-coupling reaction of sulfoxonium ylides and alkynes with water. The metal-free protocol showed an easy-to-handle nature, good functional group tolerance, and high Z-stereoselectivity, which is rare in previous cases. The proposed reaction mechanism was convincingly established by carrying out a series of control experiments, cyclic voltammetry experiments, and density functional theory (DFT) studies.

Electrochemical chemoselective hydrogenation of 1,4-enediones with HFIP as the hydrogen donor: scalable access to 1,4-diketones.

A straightforward electrochemical protocol for efficient hydrogenation of unsaturated CC bonds has been reported in an undivided cell. A series of versatile 1,4-diketones are smoothly generated under metal-free and external-reductant-free electrolytic conditions. Moreover, the tolerance of various functional groups and decagram-scale experiments have shown the practicability and potential applications of this methodology. Moreover, a range of heterocyclic compounds were easily prepared through follow-up procedures of 1,4-diketones.

SO42- ions as a nucleophilic reagent: straightforward electrochemical access to organosulfates.

An electrooxidation direct difunctionalization of alkynes with sulfonyl hydrazides has been developed for the construction of sulfonyl alkenyl sulfates in the absence of metal catalysts and a stoichiometric amount of oxidants. Notably, it is the first example to verify that SO42- ions can act as a nucleophilic reagent for the preparation of organosulfates.

Selective Electrochemical Synthesis of 9-Aryl-10-sulfonyl Substituted Phenanthrene from Alkynes and Sulfonyl Hydrazides.

An efficient electrochemical synthesis of sulfonated phenanthrenes via the reaction of internal alkynes with sulfonyl hydrazides has been established. The protocol does not require a metal catalyst or external oxidants, providing a green and mild route to functionalized phenanthrenes. Moreover, the compatibility of various functional groups and decagram-scale experimental conditions demonstrate the practicality of the electrochemical strategy.

Electrochemically Promoted [3 + 2] Annulation of Imidazo[1,2-a]pyridine with Alkynes.

The efficient electrochemically promoted [3 + 2] annulation of imidazo[1,2-a]pyridines with alkynes using traceless electrons as green reagents has been developed, leading to the synthesis of a large class of polycyclic heteroaromatics in good yields with a broad substrate scope under mild and green conditions. The scaled-up experiment, follow-up procedures, and potential biological applications show the practicability and feasibility of the electrochemical method.

[Variety of the Composition and Sources of VOCs During the Spring Festival and Epidemic Prevention in the Pearl River Delta].

Volatile organic compounds (VOCs) are the key precursors of the ozone (O3) formation processes in the troposphere and are important control objects for the coordinated governance of O3 and PM2.5. The Spring Festival of 2020 was affected by the novel coronavirus (COVID-19) pneumonia epidemic:companies stopped work and production, and traffic was restricted, providing scientific experimentation opportunities for pollutant emission reduction research. This study analyzed the variety of the composition, chemical reaction activity, and sources of VOCs in the Pearl River Delta during the Spring Festival and the epidemic control period, using real-time online monitoring data of VOCs obtained at four sites(Guangzhou, Dongguan, Zhongshan, and Duanfen)in the Pearl River Delta from January 1, 2020 to February 29, 2020. The results showed that during the Spring Festival and the epidemic control period, the average of φ (VOCs) in the Pearl River Delta was 15.89×10-9, and the maximum hourly average concentration was 45.43×10-9, values that were 44% and 60% lower, respectively, than those before the Spring Festival holiday. Among the VOCs component concentration decreases, the aromatic hydrocarbon component decreased the most, and the decrease in the urban area of the Pearl River Delta (74%) was significantly greater than that in the suburban area (56%). As a result, the contribution rate of aromatic hydrocarbons to the total VOCs was reduced to less than 10%. The analysis of the·OH reaction activity of VOCs(L·OH)and ozone formation potential(OFP)showed that the L·OH and OFP of VOCs decreased significantly in the Pearl River Delta during the Spring Festival and the epidemic control period. Compared with those before the Spring Festival holiday, the total L·OH and total OFP decreased by an average of 60% and 63% in the urban area of the Pearl River Delta, respectively. Additionally, the atmospheric oxidation had also been significantly reduced, which showed a 28% decrease in ρ(Ox). The ratio of toluene/benzene showed that the influence of industrial sources had almost disappeared during the Spring Festival and the epidemic control period, and the total points of the representative components of industrial-related solvent-use sources such as toluene, ethylbenzene, and m/p-xylene dropped by 72% to 91%. The results of this study suggest that solvent-use sources and vehicle exhaust emission sources are the current sources of VOCs that need to be paid attention to in the prevention and control of O3 pollution in the Pearl River Delta region, and the impact of petrochemical sources cannot be ignored in the work of further reducing the background concentration of O3.

Hypervalent iodine promoted the synthesis of cycloheptatrienes and cyclopropanes.

A new strategy is reported for intramolecular Buchner-type reactions using PIDA as a promotor. Traditionally, the Buchner reaction is achieved via Rh-carbenoids derived from RhII catalysts with diazo compounds. Herein, the first metal-free Buchner-type reaction to construct highly strained cycloheptatriene- and cyclopropane-fused lactams is presented. The advantage of these transformations is in their mild reaction conditions, simple operation, broad functional group compatibility and rapid synthetic protocol. In addition, scaled-up experiments and a series of follow-up synthetic procedures were performed to clarify the flexibility and practicability of this method. DFT calculations were carried out to clarify the mechanism.

Nickel-promoted oxidative domino Csp3-H/N-H bond double-isocyanide insertion reaction to construct pyrrolin-2-ones.

The first nickel-catalyzed oxidative domino Csp3-H/N-H double isocyanide insertion reaction of acetamides with isocyanides has been developed for the synthesis of pyrrolin-2-one derivatives. A wide range of acetamides bearing various functional groups are compatible with this reaction system by utilizing Ni(acac)2 as a catalyst. In this transformation, isocyanide could serve as a C1 connector and insert into the inactive Csp3-H bond, representing an effective way to construct heterocycles.

The ruthenium(ii)-catalyzed C-H olefination of indoles with alkynes: the facile construction of tetrasubstituted alkenes under aqueous conditions.

An environmentally-friendly and facile protocol for the construction of tetrasubstituted alkenes has been established with Ru(ii)-catalyzed C-H bond functionalizations under mild conditions. The method features the usage of readily available substrates, without external oxidants and additives, 100% atom economy, and excellent regioselectivity, thus enhancing the practicability of this protocol. Moreover, this transformation proceeded smoothly under aqueous conditions and could be extended to the gram scale. N-Methoxyamide, as a directing group (DG), played a vital role in the transformation.

InCl3-catalyzed 5-exo-dig cyclization/1,6-conjugate addition of N-propargylamides with p-QMs to construct oxazole derivatives.

An InCl3-catalyzed atom-economic intramolecular 5-exo-dig cyclization/1,6-conjugate addition/aromatization of N-propargylamides with p-QMs to produce oxazoles tethering diarylmethane has been successfully developed. InCl3 not only served as Lewis acid to catalyze the cyclization of propargylic amides but also activated the carbonyl of p-QMs to achieve the 1,6-addition process in a one-pot manner. The reaction has attractive features, including mild reaction conditions, broad scope of substrates, good yields, and scalability.

Fast construction of isoquinolin-1(2H)-ones by direct intramolecular C-H/N-H functionalization under metal-free conditions.

The general protocol for the synthesis of isoxazolidine-fused isoquinolin-1(2H)-ones was established with the help of bench stable hypervalent iodine reagent PIDA. Polycyclic six-, seven- and eight-membered N-heterocycles can be rapidly synthesized from available amides under metal-free conditions within 1 min at room temperature through C-H/N-H functionalization. Moreover, the protocol has the merits of broad substrate scope, atom economy and operational simplicity.

Silver-promoted regioselective [4+2] annulation reaction of indoles with alkenes to construct dihydropyrimidoindolone scaffolds.

An AgI-promoted regioselective [4+2] annulation reaction of indoles with alkenes has been established. During the transformation, N-centered radicals are generated by the oxidation of the N-H bond of N-alkoxyamides. Control experiments and DFT calculations reveal a plausible mechanism. This synergistic process achieves the direct construction of new C-C and C-N bonds under relatively mild conditions with broad substrate scope, high atom economy, and easy-to-handle nature.

N-Phenoxyamides as Multitasking Reagents: Base-Controlled Selective Construction of Benzofurans or Dihydrobenzofuro[2,3- d]oxazoles.

An efficient method to selectively construct benzofuran and dihydrobenzofuro[2,3- d]oxazole derivatives has been successfully established by means of base-controlled cyclization of N-phenoxyamides with 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1 H)-one (TIPS-EBX). N-phenoxyamides as multitasking reagents have triggered two different cascade reaction sequences. This is the first example of using TIPS-EBX for the transformation of C(sp) to either C(sp2) or C(sp3) under metal-free conditions.

One Base for Two Shots: Metal-Free Substituent-Controlled Synthesis of Two Kinds of Oxadiazine Derivatives from Alkynylbenziodoxolones and Amidoximes.

Different 1,2-migrations and cyclizations of a variety of alkynylbenziodoxolones (EBXs) and amidoximes under one-base conditions are described. This process provides an efficient protocol for the divergent synthesis of two oxadiazine derivatives via switchable selectivity of EBXs controlled by simply varying the substituents of the amidoximes, which feature transition metal-free conditions, simple execution, and high chemoselectivity.

Intramolecular dehydrogenative C-S bond coupling of thioamides to form 1,3-benzothiazines under metal-free conditions.

A novel HTIB-promoted direct intramolecular dehydrogenative C-S bond coupling reaction of thioamides has been developed to provide 1,3-benzothiazine derivatives in good yields. The reaction proceeds smoothly to reach completion at room temperature within 1 min under metal-free conditions. This protocol provides a mild and efficient strategy for the synthesis of six-membered N,S-containing heterocycles. Preliminary mechanistic studies indicate that a spirocyclic intermediate might be involved.

Construction of Benzofuran-3(2 H)-one Scaffolds with a Quaternary Center via Rh/Co Relay Catalyzed C-H Functionalization/Annulation of N-Aryloxyacetamides and Propiolic Acids.

An unprecedented synthesis of valuable benzofuran-3(2 H)-one scaffolds with a quaternary center was developed via Rh/Co relay catalyzed C-H functionalization/annulation of N-aryloxyacetamides with propiolic acids in moderate to good yields. The reaction features the simultaneous construction of the benzofuran motif containing a C2 quaternary center and a C3 carbonyl group. The preliminary mechanism study verified that the O atom of C3 carbonyl group originates from molecular oxygen.

Nickle Catalysis Enables Access to Thiazolidines from Thioureas via Oxidative Double Isocyanide Insertion Reactions.

An efficient synthesis of thiazolidine-2,4,5-triimine derivatives was developed via Ni-catalyzed oxidative double isocyanide insertion to thioureas under air conditions, in which thioureas play three roles as a substrate, a ligand, and overcoming isocyanide polymerization. The reaction is featured by employing a low-cost and low loading Ni(acac)2 catalyst, without any additives, and high atom economy. This is the first example to directly apply a Ni(II) catalyst in oxidative double isocyanide insertion reactions.

Metal-Free Direct Construction of 2-(Oxazol-5-yl)phenols from N-Phenoxyamides and Alkynylbenziodoxolones via Sequential [3,3]-Rearrangement/Cyclization.

A mild and straightforward synthetic protocol for the construction of 2-(oxazol-5-yl)phenol derivatives promoted by K2CO3 from N-phenoxyamides and alkynylbenziodoxolones at room temperature has been developed. Importantly, this protocol involves a tandem sequence that includes [3,3]-rearrangement/alkylidene carbene insertion/Michael addition/cyclization. The metal-free conditions, broad substrate scope, and simple execution make this novel protocol very attractive.

Fast Construction of 1,3-Benzothiazepines by Direct Intramolecular Dehydrogenative C-S Bond Formation of Thioamides under Metal-Free Conditions.

The first general protocol for the synthesis of 1,3-benzothiazepine derivatives was established. With the aid of bench-stable hypervalent iodine promoter fluoro-HTIB, these seven-membered heterocycles can be rapidly synthesized from readily available thioamides under air atmosphere and metal-free conditions. The transformation can be completed within 1 min at room temperature and features a broad substrate scope.

When Ethyl Isocyanoacetate Meets Isatins: A 1,3-Dipolar/Inverse 1,3-Dipolar/Olefination Reaction for Access to 3-Ylideneoxindoles.

A new CuI/1,10-phen-catalyzed reaction for the synthesis of 3-ylideneoxindoles from readily available isatins and ethyl isocyanoacetate, in which ethyl isocyanoacetate acts as a latent two-carbon donor like the Wittig reagent, is reported. A tandem procedure including 1,3-dipolar cycloaddition/inverse 1,3-dipolar ring opening/olefination allows the preparation of 3-ylideneoxindoles with broad functional group tolerance.